# Statistics Ch 7

 The flashcards below were created by user firefly501 on FreezingBlue Flashcards. Observational study Record data on individuals without attempting to influence theresponses. We typically cannot prove anything this way. Experimental study Deliberately impose a treatment on individuals and record theirresponses. Influential factors can be controlled.Observational studies of the effect of one variable on another often fail because theexplanatory variable is confounded with lurking variables.Well-designed experiments take steps to defeat confounding. Population The entire group of individuals in which we are interested but can’t usually assess directly. Parameter a number describing a characteristic of the population. Sample The part of the population we actually examine and for which we do have dataHow well the sample represents the population depends on the sample design.Statistic is a number describing a characteristic of a sample Bad sampling methods Convenience sampling & bias Convenience sampling Just ask whoever is around. Bias Opinions limited to individuals present Voluntary Response Sampling Individuals choose to be involved Bias Sample design systematically favors a particular outcome. Good sampling methods Probability or random sampling Probability or random sampling Individuals are randomly selected.Sampling randomly gets rid of bias. Simple random sample (SRS) is made of randomly selected individuals. Eachindividual in the population has the same probability of being in the sample. All possiblesamples of size n have the same chance of being drawn. SRS Simple random sample How to choose an SRS of size n from a population of size N: 1. Label2. Table B3.Stratified random sample Label Give each member of the population a numerical label of the same length. Table B Read from Table B successive groups of digits of the length you used as labels. Your sample contains the individuals whose labels you find in the table. Stratified random sample a series of SRS performed on subgroups of a givenpopulation. The subgroups are chosen to contain all the individuals with a certain characteristic.The SRS taken within each group in a stratified random sample need not be of the samesize. Caution about sampling surveys NonresponseResponse biasWording effectsUndercoverage Learning about populations from samples The techniques of inferential statistics allow us to draw inferences or conclusions about apopulation from a sample.Your estimate of the population is only as good as your sampling design Work hard to eliminate biases.Your sample is only an estimate—and if you randomly sampled again, you would probably get a somewhat different result.The bigger the sample the better. Authorfirefly501 ID137601 Card SetStatistics Ch 7 DescriptionProducing Data: Sampling Updated2012-02-25T17:13:14Z Show Answers